INTRODUCTION. 



THE following monograph of the Fresh-water Crawfishes of North 

 America is intended to form the first step in a scientific examina- 

 tion of the rich crustacean materials contained in the Museum of Com- 

 parative Zoology at Harvard College, in Cambridge. The excellent 

 monograph of the genus Callinectes, published by Mr. A. Ordway in 

 1863, is the onl^" work about Crustacea, based jjrincijDally ujjon the 

 Camljridge collection. 



Arriving in Cambridge in October, 1867, in order to take care of the 

 articulated animals belonging to the Museum, I was charged first to 

 arrange and put in order the Crustacea. Because of the almost total 

 lack of room and of working hands (the rich collections from Brazil 

 procured b}^ the Thayer Expedition having occupied all working time 

 for the last two years), but a small part had been as yet determined 

 and arranged in the rooms opened for public exhibition. The greater 

 portion of them had been stored for several years in the cellar, and 

 therefore was so situated as not to be readily accessible for a scientific 

 examination. 



The part exhibited comprised a series of three hundred and twenty- 

 seven determined species in a systematical collection, also three hun- 

 dred and thirty-seven detennined species in several faunal collections, 

 and a few types of the United States Exploring Expedition. Nearly all 

 the latter species being represented also in the systematical series, the 

 number of named species (determined mostly by Mr. Dana and Mr. W. 

 Stimpson) did not perhaps exceed five hundred. With the exception 

 of several boxes already separated, with duplicates for exchange, they 

 answered to a catalogue of nearly sixteen hinidred number's, contain- 

 ing the names of the respective localities and collectors, the dates of 

 capture, and, in some cases, the scientific determinations by Mr. W. 

 Stimpson. 



